Catalysts for the evolution of hydrogen from borohydride solution

ABSTRACT

Organic pigments are capable of catalyzing the decomposition reaction of hydrogen-rich, stabilized, borohydride solutions to generate hydrogen gas on-board an operable hydrogen-consuming device such as a motor vehicle or other combustion engine. The organic pigments are used in hydrogen generating systems and in methods for controlling the generation of hydrogen gas from metal hydride solutions.

This is a Divisional of U.S. patent application Ser. No. 11/031,233filed Jan. 07, 2005 now U.S. Pat. No. 7,591,864 which claims the benefitof priority from U.S. Provisional Application Ser. No. 60/535,293 filedJan. 09, 2004, and was supported in part by the National Aeronauticaland Space Administration (NASA), grant #NAG3-2751 and Department ofEnergy, Office of Energy Efficiency and Renewable Energy (EERE),contract #DEFC3699G010449 to University of Central Florida, FloridaSolar Energy Center.

FIELD OF THE INVENTION

This invention relates to the novel use of organic pigments ascatalysts, in particular to a catalytically controlled system for therelease of hydrogen from a hydrogen-rich borohydride solution.

BACKGROUND AND PRIOR ART

Hydrogen gas is a very desirable fuel because it can be reacted withoxygen in hydrogen-consuming devices, such as a fuel cell, combustionengine or gas turbine, to produce energy and water. The use of hydrogengas can ameliorate environmental pollution; lessen the world'sdependency on fossil fuels or petroleum; ease fears of depleted energysources.

Safe and efficient storage of hydrogen is a prerequisite for widespreadcommercial use as a fuel. U.S. Pat. No. 6,534,033 B1 to Amendola et al.,discloses the use of stabilized metal hydride solutions as an example ofa safe, hydrogen-rich storage medium. Thus, with an abundant supply ofmetal hydride solutions, research is focused on the release of hydrogenfrom the storage medium.

The class of metal hydrides known as borohydrides is known to decomposein water, in the following manner: borohydride plus water yieldsmetaborate and hydrogen gas. The chemical reaction illustrated withborohydride is:BH ₄ ⁻+2H ₂ O═BO ₂ ⁻+4H ₂.

Hydrogen-rich borohydrides are also of interest in electroconversioncells where the alkali metal-containing compound, such as borohydride isoxidized to generate electricity (U.S. Pat. No. 5,804,329 to Amendola;U.S. Pat. No. 6,468,694 B1 to Amendola; and U.S. Pat. No. 6,554,877 B2to Finkelshtain et al.). Although oxidation reactions are required togenerate electric current, the spontaneous release of hydrogen gas whenborohydrides are in contact with water is reported in each of thepatents cited above. The borohydride decomposition reaction in wateroccurs very slowly without a catalyst. Thus, catalysts become thecritical component in any hydrogen gas delivery system based onborohydride decomposition.

Catalysts used in hydrogen gas evolution or production of hydrogencompounds have been identified as amines (U.S. Pat. No. 3,923,966 toVaughan); metal derivative catalysts (U.S. Pat. No. 4,448,951 to Rupertet al. and U.S. Pat. No. 6,387,843 B1 to Yagi et al.); and transitionmetal catalysts (U.S. Pat. No. 5,804,329 to Amendola and U.S. Pat. No.6,534,033 B1 to Amendola et al.).

There is a need for a broader range of catalytic materials, so thatthere are more choices for use in hydrogen-consuming devices. Thepresent invention provides consumers with a broader choice of catalysts,which, in some cases, catalyze the hydrogen gas evolution reaction at arate exceeding that of catalysts identified in the prior art.

SUMMARY OF THE INVENTION

The first objective of the present invention is to provide a broaderselection of catalysts for the evolution of hydrogen gas fromborohydride solutions.

The second objective of the present invention is to provide a hydrogengeneration system using a low-cost, safe, stable hydrogen-richborohydride solution in conjunction with novel organic pigmentcatalysts.

The third objective of the present invention is to provide a hydrogengas generation system suitable for on-board generation of hydrogen forhydrogen-consuming devices.

The fourth objective of the present invention is to provide a hydrogengas generation system suitable for vehicular operation.

The fifth objective of this invention is to provide a novel use forreadily available and known organic pigments.

A preferred hydrogen generation system is provided with a metal hydridesolution, comprising a metal hydride, a stabilizing agent to provide apH of approximately 9 or greater and water which is then contacted withorganic pigments as hydrogen generating catalysts.

The preferred metal hydride in the hydrogen generating system of thepresent invention is selected from the group consisting of sodiumborohydride, lithium borohydride, potassium borohydride, ammoniumborohydride, tetramethyl ammonium borohydride, and mixtures thereof.

The preferred stabilizing agent in the hydrogen generating system of thepresent invention is selected from the group consisting of sodiumhydroxide, lithium hydroxide, potassium hydroxide, ammonium hydroxide,and mixtures thereof.

The preferred organic pigment catalysts are in the form of a solid,loose powder, more preferably the organic pigment is attached to asubstrate made of ceramics, cements, glass, zeolites, perovskites,fibers, fibrous material, mesh, polymeric resin and plastic.

The more preferred hydrogen generating catalysts of the presentinvention are organic pigments having an orbital structure with a lowunoccupied molecular orbital (lumo) energy and can be chosen frompyranthrenedione, indanthrene gold orange,ditridecyl-3,4,9,10-perylenetetracarboxylic diimide, indanthrene black,dimethoxy violanthrone, 1,4-diketopyrrolo-3,4C pyrrole, quinacridone,indanthrene yellow, copper phthalocyanine,3,4,9,10-perylenetetracarboxylic dianhydride, isoviolanthrone,perylenetetracarboxylic diimide, indigo and mixtures thereof.

The preferred hydrogen generating catalysts are formed by blending thecatalyst powder with a poly(methyl methacrylate) binder and fixing theblended material onto a plastic substrate.

It is preferred that the hydrogen generating system of the presentinvention be operably connected to a hydrogen-consuming device that usesa substantial portion of the hydrogen gas reaction product. Thehydrogen-consuming device can be a fuel cell, a combustion engine, a gasturbine, and combinations thereof.

A preferred method for controlling the generation of hydrogen gas from ametal hydride solution with organic pigment catalysts includesstabilizing the metal hydride in an aqueous solution, maintaining thetemperature of the solution above the freezing point and below thevaporization point of said solution, immersing a catalyst in the metalhydride solution, increasing the rate of decomposition of the metalhydride into hydrogen gas and a metal salt, and directing the hydrogengas to an operably connected, hydrogen-consuming device, such as a fuelcell, a combustion engine, a gas turbine, and combinations thereof.

The metal hydride used in the hydrogen generating process can be sodiumborohydride, lithium borohydride, potassium borohydride, ammoniumborohydride, tetramethyl ammonium borohydride, and mixtures thereof.

The hydrogen generating process uses a stabilizing agent such as, sodiumhydroxide, ammonium hydroxide, lithium hydroxide, potassium hydroxide,and mixtures thereof to adjust the pH of the metal hydride solution andorganic pigment catalysts that have an orbital structure identified by alow unoccupied molecular orbital (lumo) energy. More specifically, theorganic pigment catalysts include, but are not limited to,pyranthrenedione, indanthrene gold orange,ditridecyl-3,4,9,10-perylenetetracarboxylic diimide, indanthrene black,dimethoxy violanthrone, 1,4-diketopyrrolo-3,4C pyrrole, quinacridone,indanthrene yellow, copper phthalocyanine,3,4,9,10-perylenetetracarboxylic dianhydride, isoviolanthrone,perylenetetracarboxylic diimide, and indigo.

It was surprising and unexpected that organic pigments could be immersedin borohydride solutions in a manner that controls the rate of hydrogengas evolution suitable for on-board generation of hydrogen for vehicularapplications, such as hydrogen fuel cells or combustion engines.

Further objects and advantages of this invention will be apparent fromthe following detailed description of a presently preferred embodimentthat is illustrated schematically in the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows hydrogen gas evolution from non-buffered 0.1 M NaBH₄solution in the presence of many catalysts.

FIG. 2 shows hydrogen gas evolution from 0.1 M NaBH₄ solution bufferedat pH 11 in the presence of many catalysts.

FIG. 3 shows pH dependence of catalytic hydrogen gas evolution from 0.1M NaBH₄ solution using pyranthrenedione catalyst.

FIG. 4 shows the evolution of hydrogen gas from NaBH₄ solution at pH 11over immobilized organic pigment catalysts.

FIG. 5 is a schematic view of a hydrogen gas generation device usingLiBH₄ tablets.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Before explaining the disclosed embodiment of the present invention indetail it is to be understood that the invention is not limited in itsapplication to the details of the particular arrangement shown since theinvention is capable of other embodiments. Also, the terminology usedherein is for the purpose of description and not of limitation.

The present invention provides a novel use of organic pigments ascatalysts in a hydrogen generation system utilizing stabilizedborohydride solutions.

Table 1 is a ranking of catalysts from the fastest to the slowest forthe decomposition of sodium borohydride (NaBH₄) in a buffered solutionof pH 11. Table 1 shows that pyranthrenedione is first with a meanevolution rate of 6.5 ml of hydrogen gas per minute.

TABLE 1 Ranking of Catalysts RANK CATALYST 1 Pyranthrenedione 2Indanthrene Gold Orange 3 Ditridecyl-3,4,9,10-perylenetetracarboxylicdiimide 95% 4 Cobalt Powder (Prior Art) 5 Indanthrene Black 6 DimethoxyViolanthrone 7 1,4-Di keto-pyrrolo (3,4 C) pyrrole 8 Quinacridone 9Indanthrene Yellow 10 Copper Phthalocyanine 113,4,9,10-Perylenetetracarboxylic dianhydride 12 Isoviolanthrone 13Perylenetetracarboxyic diimide 14 Indigo

FIG. 1 shows hydrogen generation from an unbuffered aqueous borohydridesolution using organic pigments as catalysts. In FIG. 1, the evolutionof hydrogen gas is plotted for many different catalysts, includingcobalt, a catalyst known in the prior art. Five milliliters (ml) ofpurified water is adjusted to have neutral alkalinity (pH 7) prior tothe addition of one gram of sodium borohydride (NaBH₄) in the presenceof 100 milligrams (mg) of a catalyst, in the form of a loose powder,selected from the catalysts shown in Table 1. The identity of eachcatalyst in FIG. 1 corresponds to the numerical ranking in Table 1,which ranks catalytic activity in a buffered solution (pH 11).

The pigment catalyst powder is added to water, and then followed by theaddition of solid sodium borohydride. The vessel is immediately sealedexcept for a thin tube leading to an inverted graduated cylinder for gasmeasurement. It is seen that after an initial quick rise in H₂ volume,the curves tend to level out after about ten minutes. This is due to thedepletion of the borohydride content of the vessel as it decomposes, anddue to rising pH, which adversely affects the H₂ evolution rate. Thus,it is noted that the non-buffered, variably alkaline solution used inFIG. 1 affects the rate at which each catalyst influences hydrogengeneration. In the non-buffered 0.1 M NaBH₄ solution, indanthrene goldorange (No. 2) catalyzes the generation of 800 ml of hydrogen inapproximately ten minutes and can sustain the 800 ml volume of hydrogengas generation for a period of at least sixty minutes. The organicpigment catalyst, 3,4,9,10-Perylenetetracarboxylic dianhydride, alsoknown as perylene TCDA (No. 11), catalyzes the generation of 500 ml ofhydrogen in approximately ten minutes and the volume of hydrogengenerated, increases to approximately 700 ml over a period of 60minutes. Likewise, pigment catalyst (No. 3),Ditridecyl-3,4,9,10-Perylenetetracarboxylicdiimide 95% (also known asperylene diimide) outperforms cobalt, a prior art catalyst and theremainder of catalysts in Table 1.

An equal amount (100 mg) of metallic cobalt powder was employed to serveas a basis of comparison with the existing art in borohydridedecomposition catalysts.

FIG. 2 shows the rate of hydrogen production with organic pigmentcatalysts using sodium borohydride in a buffered solution with pH 11.Each catalyst is identified by the unique legend shown on the left ofthe graph. When buffered solutions are used for borohydridedecomposition, the free hydrogen ion concentration remains constant, andso H₂ evolves at a constant rate. At pH 11, the evolution rate is slowenough that it can be readily monitored. The order of activity isbasically the same for all catalysts, except for pyranthrenedione (alsoknown as pyranthrone), which is the most active catalyst. When plottingthe volume of hydrogen generated over a period of time, the graphreveals that 300 ml of hydrogen are generated in approximately 20minutes by the organic pigment catalyst, pyranthrenedione. The remainingcatalysts perform at a slower rate, generating a lower volume ofhydrogen, in a range of approximately 250 ml in a time period fromapproximately 30 minutes to approximately 80 minutes. Cobalt powder, aprior art catalyst, generated approximately 350 ml of hydrogen inapproximately 40 minutes. Thus, it is seen that a buffered solutiongives a different result for each catalyst used for generating hydrogen.A comparison of the results in FIGS. 1 and 2 shows that the rate ofhydrogen evolution during the decomposition of alkali metal borohydridesolutions is a function of several factors, including the choice oforganic pigment catalyst, the pH of the aqueous solution, andconcentration of catalyst.

FIG. 3 compares the rates of hydrogen production using sodiumborohydride and pyranthrenedione in buffered solutions in a range frompH 9 to pH 12. Using the same catalyst, the hydrogen gas evolution at pH9 is about 600 ml in less than 5 minutes, at pH 10, 400 ml of hydrogenare evolved in approximately 6 minutes; at pH 11 it takes approximately30 minutes to generate 250 ml hydrogen and at pH 12 the hydrogen evolvedis less than 50 ml in over 40 minutes. FIG. 3 graphically illustrateshow changing only the pH can be used with an organic pigment catalyst tocontrol rate of hydrogen evolution. The pH is a measure of free hydrogenion (hydronium ion) concentration in the solution. A first orderdependence of gas evolution rate with pH is observed. There is aninverse relationship between pH and the free hydrogen ion concentration.Therefore, as pH increases, the H₂ evolution rate decreased, as shown inFIG. 3. Each unit increase in pH translates to an order of magnitudedecrease in hydrogen ion concentration. Consequently, the slope of thegas evolution curve decreased by nearly an order of magnitude with eachunit increases of pH.

FIG. 4 shows the varying rates of hydrogen gas evolution from sodiumborohydride (NaBH₄) solution catalyzed by organic pigments immobilizedon polycarbonate substrates and buffered to a pH 11. A plainpolycarbonate strip and select group of organic pigment catalystpowders, are individually blended with a poly(methyl methacrylate)binder and fixed onto a plastic substrate. The resulting gas evolutioncurves for the organic pigment catalysts show that the immobilizedcatalyst powders are still active for hydrogen evolution. Afterapproximately 1 hour immobilized pyranthrenedione generates 250 ml ofhydrogen gas; indanthrene gold orange immobilized on a substrategenerates approximately 240 ml of hydrogen gas in 75 minutes andimmobilized perylenetetracarboxylic diimide 95% catalyzes the evolutionof hydrogen at a slightly slower rate, 225 ml in approximately 80minutes. FIG. 4 provides a further example of how the organic pigmentcatalysts can be used to control the rate of H₂ evolution.Immobilization of the selected catalysts did not change the activityranking for the same catalysts in loose powder form.

The importance of the use of an immobilized catalyst is shown in thedesign of a hydrogen supply system based on lithium borohydride andshown in FIG. 5. A prototype hydrogen supply system is shown in FIG. 5.Tablets of compressed borohydride powder, 10 are loaded into ahorizontal canister equipped with a spring-loaded plunger 11. A pHelectrode 12, pressure gauge 13, or other sensor detects the state of H₂evolution. Alternatively, the throttle of an H₂-fueled vehicle could becoupled to the plunger to control the rate of mixing. The pH andtemperature of the solution can be controlled so that the backgroundrate of H₂ evolution in the absence of catalyst can be minimized.

As learned from FIG. 4, an immobilized catalyst 14, is fastened onto theend of an armature 15, which is manipulated by a gear wheel 16, or otheradjustment mechanism so that the immersion depth of the catalyst 14 intothe borohydride solution can be varied at will. During high fuelconsumption modes, such as highway driving or acceleration in general,the catalyst strip can be lowered further into the borohydride solutionto expand the total area that is performing the gas-evolving borohydridedecomposition reaction.

There are many advantages to the present organic pigment catalysts,including, but not limited to, increased utilization of known materials,versatility, reliability, accuracy of hydrogen release and economy inmaterial consumption and fuel production.

While the invention has been described, disclosed, illustrated and shownin various terms of certain embodiments or modifications which it haspresumed in practice, the scope of the invention is not intended to be,nor should it be deemed to be, limited thereby and such othermodifications or embodiments as may be suggested by the teachings hereinare particularly reserved especially as they fall within the breadth andscope of the claims here appended.

1. A method for controlling the generation of hydrogen gas from a metalborohydride solution with organic pigment catalysts, comprising:selecting a hydrogen-rich borohydride; adding the borohydride to anaqueous alkaline solution; stabilizing the borohydride in the aqueousalkaline solution; maintaining the temperature of the solution above thefreezing point and below the vaporization point of said solution;immersing a catalyst strip consisting of an organic pigment selectedfrom the group consisting of pyranthrenedione, indanthrene gold orange,ditridecyl-3,4,9,10-perylenetetracarboxylic diimide, indanthrene black,dimethoxy violanthrone, 1,4-diketopyrrolo -3,4C pyrrole, quinacridone,indanthrene yellow, 3,4,9,10-perylenetetracarboxylic dianhydride,isoviolanthrone, and perylenetetracarboxylic diimide, in the form of asolid, loose powder immobilized on a substrate selected from the groupconsisting of ceramics, cements, glass, zeolites, perovskites, fibers,fibrous material, mesh, polymeric resin and plastic, wherein thecatalyst strip is manipulated so that an immersion depth of the catalystinto the borohydride solution is varied to expand the total area that isperforming the hydrogen-gas evolving borohydride decomposition reactionrepresented by the equation, BH₄ ⁻+2H₂O BO₂ ⁻+4H₂; increasing the rateof decomposition of the metal borohydride into hydrogen gas and a metalsalt; and directing the hydrogen gas to an operably connected,hydrogen-consuming device.
 2. The method of claim 1, wherein the metalborohydride is selected from the group consisting of sodium borohydride,lithium borohydride, potassium borohydride, ammonium borohydride,tetramethyl ammonium borohydride, and mixtures thereof.
 3. The method ofclaim 1, wherein the stabilizing step is by the addition of astabilizing agent selected from the group consisting of sodiumhydroxide, ammonium hydroxide, lithium hydroxide, potassium hydroxide,and mixtures thereof.
 4. The method of claim 1, wherein the operablyconnected, hydrogen-consuming device is selected from the groupconsisting of a fuel cell, a combustion engine, a gas turbine, andcombinations thereof.